This invention relates to an engine plant comprising a plurality of turbocharged combustion engines having each an individual charging air system and an exhaust gas system, and of the type in which the charging air systems of the individual engines are interconnected by means of a closeable conduit, and in which control members are provided for opening and closing a stop valve provided in the conduit in dependence on the working condition of an associated engine.
Such a plant has been described in Applicants' U.S. application Ser. No. 922,339, filed on Oct. 23, 1986, now U.S. Pat. No. 4,787,207. The novel feature of the plant dealt with therein consists in the pipe connection between the charging air systems of the engines which makes it possible to utilize the surplus air generated by the turbocharger of a loaded engine for increasing the charging air pressure of an unloaded engine. In this context an unloaded engine is an engine working at less than about 25% of its maximum load, while a loaded engine is an engine working at about 50% to 100% of its maximum load.
The predominant problem is that the charging air pressure generated by the turbocharger of an unloaded engine at one time falls below the exhaust gas pressure so that exhaust gas may blow back into the air and gas passages of the engine and there cause problems in the form of increasing contamination. The reason why said problem may advantageously be solved by the pipe connection between the individual charging air systems is that the turbocharger of a loaded engine within said working range generates a considerable amount of surplus energy in the form of pressurized charging air.
For the purpose of controlling the supplementary supply of charging air a stop valve is provided in the mutual pipe connection upstream of one or more of the engines. Said valve is adapted to open and close in dependence on the actual working situation of the associated engine which is in practice determined by a comparison between the instantaneous values of the charging air pressure and the exhaust gas pressure, respectively. If the charging air pressure exceeds the exhaust gas pressure, supplementary charging air is not needed and the valve is therefore kept closed. If, on the contrary, the exhaust gas pressure exceeds the charging air pressure, a supplementary supply of charging air is needed and the valve must therefore be opened.
As mentioned, the control of the valve is based on a comparison between the charging air pressure and the exhaust gas pressure of the associated engine. Consequently, it is of vital importance as regards a correct control of the valve that a reliable and exact measuring of the proportion between said two pressures is available. Such a measuring may in principle be effected by a common differential pressure guage. In practice it has, however, turned out to be impossible to apply such a device successfully. Firstly, the conduit connecting the pressure gauge with the exhaust gas receiver was rapidly blocked by soot and condensed water and, secondly, it turned out to be complicated as well as expensive to manufacture a pressure gauge that is both sufficiently accurate at a differential pressure of a few millibars and which at the same time is capable of standing differential pressures up to about 1 bar.